1. Field of the Invention
The invention relates to a variable valve apparatus of an internal combustion engine and, more particularly, to an internal combustion engine variable valve apparatus including a phase variation actuator that varies the rotation phase of a camshaft and a cam displacement actuator that displaces the camshaft in the direction of a rotating axis of the camshaft.
2. Description of Related Art
Phase variation type variable valve apparatus capable of varying the relative rotation phase between a camshaft and a crankshaft, that is, an engine output shaft, are conventionally known. Such a phase variation type variable valve apparatus has a first rotating body that is connected to a drive-transmission wheel for transmitting rotation from the crankshaft, such as a cam sprocket, a cam pulley, or the like, so that the first rotating body is rotatable together with the drive-transmission wheel, and a second rotating body that is connected to the camshaft so that the second rotating body is rotatable together with the camshaft. The variable valve apparatus further has a phase variation actuator for turning the first and second rotating bodies relative to each other through the use of, for example, a vane construction or a gear connecting construction having helical splines. Using the actuator, the variable valve apparatus varies the relative rotation phase between the crankshaft and the camshaft so as to vary the valve timing of the engine valves that are opened and closed by rotation of the camshaft.
Also known is a cam displacement type variable valve apparatus that displaces a camshaft in the direction of a rotating axis thereof, the camshaft being provided with three-dimensional cams whose cam profile shape varies in the direction of the rotating axis. In the cam displacement type variable valve apparatus, the camshaft is displaced in the direction of a rotating axis thereof to change the cam profile of each three-dimensional cam at the site of contact with the valve lifter of the corresponding engine valve, by using an actuator (cam displacement actuator) of, for example, a hydraulic drive type or the like, whereby the characteristic of the engine valves is changed.
Furthermore, a variable valve apparatus having both a phase variation actuator and a cam displacement actuator as described above is disclosed in Japanese Patent Application Laid-Open No. 11-153009. In such a variable valve apparatus, it is necessary to connect a camshaft to the phase variation actuator so that the camshaft is slidable in the direction of a rotating axis thereof, in order to allow the cam displacement actuator to displace the camshaft.
FIG. 9 shows a sectional structure of a phase variation actuator and its peripheral portion of a variable valve apparatus having a phase variation type valve variable mechanism and a three-dimensional cam type variable valve mechanism.
As shown in FIG. 9, a cam sprocket 113, a journal 114 and a phase variation actuator 119 are provided at a distal end portion of a camshaft 110 having a three-dimensional cam 111. The cam sprocket 113 is a drive-transmission wheel that is drivingly connected by a chain to a crankshaft, that is, an engine output shaft of an internal combustion engine. The cam sprocket 113 is rotatably supported to the engine by the journal 114. Rotation of the cam sprocket 113 is transmitted to the camshaft 110 via the phase variation actuator 119.
The phase variation actuator 119 has an outer rotor (first rotating body) 121 that is connected to the cam sprocket 113 so that the outer rotor 121 is rotatable together with the cam sprocket 113, and an inner rotor (second rotating body) 120 that is connected to the camshaft 110 so that the inner rotor 120 is rotatable together with the camshaft 110. The outer rotor 121 is disposed radially outwardly of the inner rotor 120 (relative to the rotation axis) so that the outer rotor 121 and the inner rotor 120 have one and the same rotating axis and are rotatable relatively to each other.
The phase variation actuator 119 as shown in FIG. 9 is a generally-termed vane type phase variation actuator. The phase variation actuator 119 turns the rotors 120, 121 relative to each other based on adjustment of pressure of oil introduced into liquid chambers 123 provided in slide-contact portions of the inner rotor 120 and the outer rotor 121. By changing the relative rotation phase between the cam sprocket 113 connected to the outer rotor 121 and the camshaft 110 connected to the inner rotor 120, the phase variation actuator 119 changes the valve timing of the engine valves, which are opened and closed based on rotation of the camshaft 110.
A distal end portion of the camshaft 110 is inserted into the inner rotor 120 of the phase variation actuator 119 so that the distal end portion is slidable along an inner peripheral portion of the inner rotor 120 in the direction of a rotating axis thereof. The inner periphery of the inner rotor 120 and the outer periphery of the camshaft 110 have splines 112, 117, respectively. Thus, the phase variation actuator 119 employs a connecting construction wherein via meshing of the splines 112, 117, the inner rotor 120 and the camshaft 110 are connected so that they are rotatable together and so that the camshaft 110 is allowed to be displaced in the direction of the rotating axis.
In the example shown in FIG. 9, the phase variation actuator 119 further has, inside thereof, a sub-gear 130 for preventing production of noises of tooth impacts between the splines 112, 117 that would otherwise be caused by torque fluctuations on the camshaft 110 involved in the opening and closing of the engine valves. The sub-gear 130 is disposed between the distal end portion of the camshaft 110 and the inner rotor 120.
An outer periphery of the sub-gear 130 has external splines 131 whose tooth trace extends in the direction of the rotating axis. An inner periphery of the sub-gear 130 has internal splines 132 whose tooth trace extends in a direction diagonal to the rotating axis. The sub-gear 130 is connected to the inner rotor 120 by meshing between the external splines 131 and the internal splines 117 formed in an inner periphery of the inner rotor 120. The sub-gear 130 is connected to the camshaft 110 by meshing between the internal splines 132 and external helical splines 118 provided in an outer periphery of a distal end portion of the camshaft 110.
The sub-gear 130 is urged in a direction of the rotating axis by an urging member 133, such as a wave washer (a washer having undulations) or the like. Via the helical-splines 118, 132, the sub-gear 130 converts the force from the urging member 133 into forces in rotating directions, thereby urging the inner rotor 120 and the camshaft 110 in such directions as to turn relative to each other. In this manner, the sub-gear 130 eliminates backlashes between the splines 112, 117, thereby substantially preventing noises of impacts between spline teeth.
Thus, since the camshaft 110 and the inner rotor 120 of the phase variation actuator 119 are connected by meshing between the splines 112, 117 extending in the direction of the rotating axis thereof, the camshaft 110 is allowed to be displaced in the direction of the rotating axis while the camshaft 110 and the inner rotor 120 are integrally rotatably connected.
However, if this connecting construction is adopted, there is a possibility that the phase variation actuator 119 may have an increased diameter because the camshaft 110 needs to be inserted into the phase variation actuator 119 and the splines 112, 117 need to be formed for connection between the camshaft 110 and the phase variation actuator 119. In the case of the vane-type phase variation actuator as mentioned above, in particular, an increased diameter of the phase variation actuator 119 is inevitable because the liquid chambers 123 having sufficient capacities are formed radially outwardly of the inner rotor 120, into which the camshaft 110 is inserted.
Furthermore, if a construction using the sub-gear 130 for preventing spline impact noises as described above is adopted, the need to dispose the sub-gear 130 and the like within the phase variation actuator 119 further increases the diameter of the phase variation actuator 119.
Thus, according to the conventional art, if a camshaft is connected to a phase variation actuator so that the camshaft is allowed to be displaced, the phase variation actuator 119 inevitably has an increased diameter, so that drawbacks, such as a degraded installability, an increased weight, and the like, result.